1. Field of the Invention
This invention relates to a duplex pipette for taking in and letting out two kinds of liquid, and more particularly to such a duplex pipette which is advantageous for use together with an ionic activity measuring instrument.
2. Description of the Prior Art
In Japanese Unexamined Patent Publication Nos. 58(1983)-211648 and 59(1984)-30055, and Japanese Patent Application No. 59(1984)-11744, for instance, there is disclosed an ionic activity measuring instrument for potentiometrically measuring ionic activity or concentration of a specific ion contained in aqueous liquid samples such as body fluid (blood, urine, saliva and the like), liquors, city water, beverages and the like.
Generally, the ionic activity measuring instrument includes a pair of ion selective electrodes having, as the outermost layer, an ion selective layer which exhibits selective response to a specific ion. The ion selective electrodes are supported between an upper frame and a lower support frame. The upper frame is provided with a pair of liquid deposition holes each opposed to one of the ion selective electrodes and a porous bridge member (preferably, of twisted yarn) for establishing an electrical contact between a liquid sample deposited in one of the liquid deposition holes and a control liquid deposited in the other liquid deposition hole is generally mounted on the upper frame. When a plurality of ion selective electrodes are provided, a pair of porous liquid distributor members are provided between the ion selective electrode pairs and the upper frame to connect the liquid deposition holes and the ion selective electrodes.
For example, when three pairs of ion selective electrodes respectively exhibiting selective response to Na.sup.+, K.sup.+ and Cl.sup.- are provided, a control liquid in which the activities of these ions are known is deposited in one of the liquid deposition holes and a liquid sample in which the activities of these ions are to be detected is deposited in the other liquid deposition hole. The control liquid and the liquid sample penetrate into the corresponding porous liquid distributor members and reach the corresponding ion selective electrodes. Further, the two liquids are brought into contact with each other near the middle of the porous bridge member to establish an electrical contact. This produces a potential difference between each pair of ion selective electrodes, the value of the potential difference depending upon the difference in the activity of the corresponding ion between the liquid sample and the control liquid. By measuring the potential difference and referring to a calibration curve obtained in advance from the known activities of Na.sup.+, K.sup.+ and Cl.sup.- in the control liquid according to Nernst equation, the activities of these ions in the liquid sample can be known.
Such an ionic activity measuring instrument is very useful in analyzing aqueous liquid samples or in clinical analysis of liquid samples taken from the human body such as blood since the ionic activities in the liquid sample can be easily measured by depositing small amounts of the liquid sample and the control liquid.
When measuring ionic activity in a liquid sample using the ionic activity measuring instrument, it is preferred that the liquid sample and the control liquid be substantially simultaneously deposited in the liquid deposition holes. Further, in the case of measuring ionic activity in a body fluid, it is preferred that the body fluid be taken directly from the body and be deposited in one of the liquid deposition holes simultaneously with deposition, in the other liquid deposition hole, of the control liquid which is separately taken.
The liquid sample and the control liquid can be simultaneously taken in or let out by using a duplex pipette having a pair of cylinders and a pair of pistons respectively received in the cylinders. However, the distance between the liquid deposition holes of the instrument is 10 mm at most, and accordingly, if the distance between the tips of the cylinders is selected to conform to the distance between the liquid deposition holes, it will become very difficult to take in the control liquid and the liquid sample from bottles, for instance, and especially to take a liquid sample directly from a biological body. Further, it would be convenient if the two pistons can be operated either integrally or separately.